HR: 1340h
AN: SA43A-1106    [Abstracts]
TI: Structure and Effects of Gravity Waves in the Thermosphere From Lower Atmospheric Sources
AU: * Vadas, S L
EM: vasha@cora.nwra.com
AF: Colorado Research Associates, a division of NorthWest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301 United States
AB: Gravity waves from lower atmospheric sources such as deep convection can propagate into the thermosphere if they avoid evanescence and critical level filtering in the lower atmosphere. Some of these gravity waves have large vertical wavelengths and high frequencies, allowing them to propagate to high altitudes within the thermosphere before dissipating. Dissipation by molecular viscosity and thermal diffusivity is described via implementation of a new anelastic dispersion relation. Solar cycle effects are important because gravity wave dissipation depends on the inverse density which increases more slowly as the background temperature increases. Additionally, gravity wave vertical wavelengths increase as the background temperature increases. Together, these effects increase the gravity wave penetration altitude and alter the gravity wave structure within the thermosphere. At extreme solar minimum whereby the thermosphere is the coolest, gravity waves from lower atmospheric sources may penetrate to altitudes of ~ 200 km, while during active solar conditions, these gravity waves may penetrate to altitudes of ~ 250-300 km instead. Although not well understood at present, the dissipation of these gravity waves and subsequent forcing of the thermosphere may lead to seeding of plasma instabilities and spread-F bubbles commonly observed in the thermosphere at these altitudes and scales.
DE: 0358 Thermosphere: energy deposition (3369)
DE: 3314 Convective processes
DE: 3334 Middle atmosphere dynamics (0341, 0342)
DE: 3369 Thermospheric dynamics (0358)
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005